This includes, for example, serial coating of vehicle bodies and parts thereof with electrostatic or other atomisers including rotary atomisers, air atomisers etc., which apply the coating material using an automatically controlled metering device. Here, the term metering device generally includes volumetric metering devices, for example geared pumps or plunger-type metering mechanisms, which can be driven by a controllable motor such that the material quantity applied by the atomiser (instantaneous flow rate) can be adjusted during application as requested depending for example on the respective workpiece regions and other parameters, as elucidated for example in EP 1 314 483 A2 or DE 691 03 218 T2. The volumetric metering is typically performed by controlling the rotational speed of a geared pump or the piston speed of a plunger-type metering mechanism.
In many cases, gear metering pumps are advantageous for reason of compactness, continuous paint supply and cost benefits.
In contrast, plunger-type metering mechanisms have the benefit of higher metering precision by avoiding slippage between the gear pair and the socket housing of gear metering pumps, and in electrostatic painting devices, in which high-voltage insulation is required between the atomisers and their earthed supply system, the required electrical potential isolation can be attained by the intermittent paint delivering operation of a plunger-type metering mechanism. Further benefits will be explained.
As described in EP 1 772 194 A2, it may further make sense to connect a container serving as an interim paint storage repository of an electrostatic painting device upstream the plunger-type metering mechanism, which is already filled with the new colour in order to reduce the colour exchange time required during colour changes, while painting continues with the previous colour from the plunger-type metering mechanism. This storage vessel can also be defmied as a component of a metering device in terms of the exemplary illustrations. To drain the storage vessel, it can also include a plunger in the cylinder.
In place of volumetric metering, a paint pressure controller, e.g. in accordance with EP 1 287 900 A2, or in accordance with EP 1 34 6 775 A1, the main needle valve of the atomiser can serve as the final control element of a regulator circuit to control the paint quantity or flow rate and thus serve as a metering device.
EP 1 502 658 A1, DE 101 15 463 A1, DE 101 36 720 A1 and DE 695 10 130 T2 generally disclose metering devices incorporated into the atomiser.
For the case that an atomiser shall apply coating material with a large number of colours, which however may for example be limited by a paint circulation system, and a colour change shall be performed in the shortest possible time, colour-changer valve arrangements referred to as colour changers, are usually inserted in block assembly (i.e. as a mechanical unit), which connect the numerous colour inlets with the colour outlet leading to the atomising member via a central channel. Based on its usual modular assembly they can be adjusted to a differing number of selectable colours. Typical modular colour changers for wet paint, for example, are generally disclosed by DE 198 36 604 A1 and DE 198 46 073 A1, while a colour changer for powder paint similar in principle is described in DE 601 03 281 T2. For instance, DE 199 51 956 A1 relates to the flushing of colour changers. Such colour changers are typically connected upstream of gear or plunger metering devices or, where applicable, the mentioned paint storage vessel.
If only few colours are required, it is also possible to mount a colour changer into the atomiser, where applicable with a metering device downstream thereof (EP 1 502 658 A1), to shorten the distance to flush from the colour changer to the application member, such as the bell cup of a rotary atomiser, during a colour change. For this purpose, effort has been made to construct particularly compact colour changers (EP 1 502 659 B1), which is particularly important, if colour changers are required in a double assembly, which, as is well known, share paint supply lines and are connected with the application member via separate colour sections. The installation of a colour-changer valve arrangement in practice also referred to as ICC technology (Integrated Colour Changer) into the atomiser has the advantage of significantly reducing the paint and flushing agent losses during colour change. In case of painting car bodies, for example, the losses during colour changes from approx. 45 ml paint per atomiser and colour change with conventional colour change technology are reduced to only approx. 4 ml. A similar reduction is obtained for flushing agent losses. Moreover, the duration of colour change in typical cases can be reduced by half, from around 12 to 6 seconds, leading to a capacity increase of the coating facility of around 5-10% or for example 30-60 vehicles daily.
Due to the space required for the colour changer and the paint supply lines into the atomiser, the reduced number of selectable colours is disadvantageous in known systems with colour changers mounted into the atomiser. In place of supplying paint via one of the conventional colour changers, i.e, a modular colour change block with an outlet channel shared by the paints, the paints can also be supplied e. g. directly from circulation lines to the application member through respective paint lines each leading into the atomiser via colour valves located in the atomiser, for each of the paints being provided a separate metering device, which consequently is not to be flushed during a colour change and a greater number of less frequently required paints (so-called Low-Runners) being possible to connect via an external colour changer, as described in the German patent application 10 2006 022 570.8 of 15 May 2006 and in the patent application PCT/EP2007/003874 of 2 May 2007, the complete content of which is hereby included in the current description. The number of selectable frequently required paints (High-Runner), however, is also limited here by the available space in the atomiser, the lead through of paint lines via the wrist of the painting robot and by the space required for their assembly on the robot in upstream connection of metering devices.
Special colour supply systems offer the advantage of an unlimited number of applicable colours, in which the colours are not coming out of circulation lines, but produced in a paint mixing shop and lead to the atomiser via a colour changer. These systems, however, are relatively expensive and have considerable colour change losses in comparison to circulation line systems.
As was previously mentioned, in general, colour changers in paint shops are common, since, as is well known they allow swift changing from one paint to another during painting operation. However, they have the main disadvantage of unavoidable paint losses during flushing of the larger or smaller central channel with each colour change. After optimising the paint losses in pigged lines, metering devices etc., colour changers often represent the element of the coating facility with the most individual losses. The colour change loss is larger, the larger the diameter of the central channels is selected, to enable a larger quantity of paint to be channelled in a shorter time through the colour changer, which may be desirable for various reasons (special colour supplies, tank technology, higher paint quantities, shorter cycle times for consecutive workpieces, higher viscosities etc.). In addition, the colour change losses increase with the number of connected paints and the resultant length of the central channel, meaning that the number of colours must often be undesirably limited.
To avoid colour change losses in conventional colour changers, colour change systems operating based on the docking principle were developed, in which the paint lines provided for the various colours are connectable by mechanically movable valve elements to a line leading to the atomiser (EP 1 245 295 A2, DE 100 64 065 A1 or DE 601 11 607 T2). With these paint interfaces, paint savings (of typically 10 ml for each colour change) can be attained in comparison to conventional colour changers, however, they have various practical disadvantages such as complex motion control for starting up the connection positions, high maintenance requirement, flushing of the interface, paint drying out at the interface, leakages etc.
One proposed solution to the problem of reducing paint losses during a colour change is provided by the colour changer described in EP 1 502 657 A2, the central channel of which is sub-divided into flushable sections, the High-Runner paints often required, i.e. those with a high usage volume, being connected in the front section at the colour outlet, while at the rear, the less frequently required (Low-Runner) paints are connected in the section opposite to the colour outlet. While the often required front section can be continually flushed independently of the rear section, the less frequently required section can be flushed together with the other section. Since, as with conventional colour changers, during a colour change no longer the entire central channel is flushed, losses of paint and flushing agent are reduced. However, the persistent colour change losses are particularly undesirable for colours that are often required.
After the outlet from the colour changers, a paint pressure controller is usually located, which provides initial pressure control of a metering pump or, as was explained previously, which can act as the final control element for adjusting the paint quantity. The clearance volume of this paint pressure controller must be flushed with each colour change.
Based on the above-described state of technology, such as EP 1 502 658 A1 for example, one object of the present disclosure is to provide a coating apparatus or devices that can be used for the coating of workpieces particularly with different frequently required colours, which allow a colour change with minimal or low losses of paint, flushing agent and time.